Japanese researchers at Hokkaido and Kobe universities have discovered a method to produce a key component of lithium-ion batteries (LIB) at much lower temperatures and in a much shorter time than the currently employed methods. The component is layered lithium cobalt oxide (LiCoO2), which is used to make the cathodes for LIB used in handheld electronic devices.
The current methods of synthesising LiCoO2 require temperatures greater than 800 °C and take from 10 to 20 hours to finish. The new method works at temperatures of 300 °C and can require times of as short as 30 minutes.
“Lithium cobalt oxide can typically be synthesised in two forms,” explained Hokkaido University Chemistry Department's Professor Masaki Matsui. “One form is layered rocksalt structure, called the high-temperature phase, and the other form is spinel-framework structure, called the low-temperature phase.”
The new method developed by Matsui and his colleagues uses, as its starting materials, cobalt hydroxide and lithium hydroxide. To these are added sodium hydroxide or potassium hydroxide. These compounds were subject to a number of high-precision experiments, under a range of conditions, to produce layered crystals of LiCoO2. The reaction pathway that resulted in the formation of the crystals was also determined. The researchers called their process the hydroflux process.
“By understanding the reaction pathway, we were able to identify the factors that promoted the crystal growth of layered LiCoO2,” he reported. “Specifically, the presence of water molecules in the starting materials significantly improved crystallinity of the end product.”
The electrochemical properties of the layered LiCoO2 were also measured. These measurements established that these properties were only very slightly inferior to those of commercially-available LiCoO2, produced by the current high-temperature methods.
“This work is the first experimental demonstration of the thermochemical stability of layered LiCoO2 at low temperatures under ambient pressure,” he pointed out. “Our development of this hydroflux process will enable energy-saving measures in various ceramic production processes. Our immediate next steps will be the improvement of the hydroflux process based on our understanding of the reaction pathway.”